Chapter 8. Redundancy

PowerSmtp makes sure that the redundancy target is met before announcing to the sending mailserver that the message was properly received. In this way, messages are always stored at at least the configured minimum redundancy.

group

Each backend is assigned to a group. Backends within a group do not generate redundancy - this can be used to make sure that email is spread over different physical locations so that each site has a copy of all articles.

Multiple partitions or filesystems residing withing a same host are also candidates to reside in the same group.

Priority

Data is always stored on the highest-priority available host. By assigning different priorities, it is possible to have 'hot spare' servers which can instantly take the place of failed or replaced boxes.

Load & diskspace

Given equal priorities, powersmtp can be instructed to choose a random server, or prefer the one with the most diskspace available or the one with the lowest load.

Your choice will depend on the workload presented.

8.1. Goals

It is important to determine what targets we want to meet. PowerMail tries to maximize perceived uptime - users must at all times be able to access their mailboxes, which should contain as much of their mail as possible. Access to POP is never disabled.

Mail delivery however is halted as soon as the minimum configured redundancy cannot be guaranteed, remote mailers will have to wait until more backends become available. As this is not directly perceived by the user, disabling deliveries is preferred over allowing non-redundant deliveries.